Tube bending mandrel



July 5 1955 c. w. PlNKr-:RTON ET AL 3,258,956

TUBE BENDING MANDREL Filed Feb. 1.1, 1963 INVENTOR. CARL W P/NKERTON FRANC/S J. LANDWEHR BY j Way/A Kans., assignors to Boeing Airplane Company, Wichita, g

Kans., a corporation of Delaware Filed Feb. 11, 1963, Ser. No. 257,666 4 Claims. (Cl. 72-466) This invention relates to a liexible mandrel for use when bending tubes.

One of the objects of this invention is to provide a novel and improved tube bending mandrel that is easy and economical to manufacture, readily inserted into a bendable tube, and relatively easily removed after the tube has been bent to a diameter that may be smaller than unity, and/ or provides a tube bend surface that is smooth, uniform, of substantially constant diameter, and accordingly has a circular configuration free of wrinkles or dents particularly on the inside radius of the bend.

Another object of the invention is provision of an improved iiexible ball mandrel useful as an accessory to tube bending apparatuses and having novel interconnected and telescoped Iball segments that aid in the prevention of deformation of thin-walled tubing during bending, and that iron out deformations of a tube wall to give a smooth interior iinish when Withdrawn from a tube that has been bent.

Another object of the invention is provision of a novel ball mandrel comprising a rugged linkage having a long life expectancy.

Another object of the invention is the provision of a novel fiexible ball mandrel for tube bending having ball portions that are journaled one each on interconnected journal -shaft segments whereby the balls are free to turn so as to provide uniform wear over the external periphery thereof, the balls being supported by said journal shaft segments against deformation of its circular configuration.

The invention further resides in certain novel features of construction, combinations, and arrangements of parts, and further objects and advantages of the invention will be apparent to those skilled in the art to which it pertains from the following `description of the present preferred embodiment thereof described with reference to the accompanynig drawings, which form a part of this specification, wherein the same reference numerals indicate corresponding parts throughout the several views, and in which:

FIG. l illustrates an actual tube bending operation, a bent tube being sectionalized in order to show the invention in a liexed condition therein;

FIG. 2 is a plan View of the invention showing certain details thereof in section;

FIG. 3 is a cross-sectional view along line 3-3 in FIG. 2;

FIG. 4 is a cross-sectional view along line 4 4 in FIG. 2; and

FIG. 5 is a sectional view of the invention, similar to FIG. 2, but with the invention rotated through 90.

It is to be understood that the invention is not limited to the details of construction and arrangements of parts shown in the drawings, and hereinafter described in detail, but is capable of lbeing otherwise embodied and of being practiced and carried out in various ways. It is to be further understood that the terminology employed herein is for the purpose of description and there is no intention to herein limit the invention beyond the re quirements of the prior art.

Referring to FIG. 1, reference numeral indicates generally a tube having a bendable wall. One end of the tube 10, that is being bent around a grooved forming block 12, is attached thereto by -means of a suitable retaining device, such as a bolted clamp at the end 16 of I United States Patent O ice the tube 14. The invention, indicated generally lby the reference numeral 20, is disposed in an operative position within the radiused end of the tube 10. The invention, hereinafter referred to as a tube bending mandrel 20, has a solid rectilinear cylindrical rod-like shank 21 disposed within and closely conforming to the internal wall surface of the tube 10. One end of the shank 21 is internally threaded to receive a threaded stud portion of a tension rod 22. The other end of the tension rod 22 is connected to a fixed support member 23 by means of a flange 24 fixed to the rod 22, and stud bolts 25 fixing the flange 24 to the member 23.

Referring to FIG. 2, the shank 21 of the tube bending mandrel 20, has internal threads 26 on its outer end to threadedly receive the tension rod 22, while at the other end of the shank there is an assembly comprising a plurality of interconnected links carrying telescoped rotatably journaled balls 28 connected to the shank 21 lby means of a dowel pin 30.

A desirable feature of this invention is that each of the balls 28 are identical in construction and are thus interchangeable. Each ball 28 comprises a segment of a sphere and has a semispherical peripheral surface 31. Each Eball 28 has a central bore 32 for permitting the insertion of a linkage therethrough. The linkage will be described later. Each vball 28 has a coaxial cylindrical counterbore 33 on one end, referred to hereinafter as an outer end, adapted to journal on a short journal shaft or external cylindrical peripheral shoulder portion 34 forming an integral part of each link. The other or inner end of each ball 28 has a spherically rounded concave recess 35 formed therein. As indicated in FIG. 2, the radius R of each ball surface 31 is substantially one half of the diameter of tube 18 minus the wall thickness thereof. The axial thickness or length of each ball 28 taken along the central longitudinal axis of the mandrel 20, FIG. 2, is approximately equal to the radius R plus the amount of overlap desired which, for purposes of illustrated, is one-sixteenth of an inch. An inner end of each ball 28 overlaps the outer end of an adjacent ball turnably disposed within the juxtaposed inner end of the adjacent outer ball 28. The distance, therefore, between the centers of each ball 28 is approximately the radius R. Similarly, the inner end of the mandrel shank 21 is hemispherically radiused. Preferably, the distance 'between the inner terminal end of the shank 21 and the center of the pin 30 is equal to one half of radius R plus, for example, one-sixteenth of an inch. Accordingly, the distance between the radius center and the center of the pin 38 in th-e ball end of the shank 21 and the radius center of adjacent ball 28 is equal to radius R.

Each of the three balls 28 are linked together by means of links 40, 41, and 42 to the pin 30 in the shank 211. The

links 40, 41, and 42 each have identically-shaped primary journal bearing shaft segments 34 preferably of slightly greater longitudinal thickness than the counterbores 33 of the balls 28, which are journaled thereon. Additional or secondary journal bearing segments 44 are adapted to journal t-he walls of bore-s 32 of the balls 28 thereon. The link 40 is an end link having a tongue 45 adapted to be pivotally connected in a slot 46 in the link 41 by means of a cylindrical pivot pin 47. The pin 47 is slidably fitted in the bifurcated portion or legs of the link 41 formed by the slot 46. The pin 47 does not extend beyond the smaller journal surface 44 of the link 41.

Similarly, the link 41 is connected to the link 42 by means of a tongue 48 and a pivot pin 50. The tongue 48 is thicker than the tongue 45. The ends of the pin 50 do not protrude beyond the smaller journal surface 44 of the link 41. The tongue 48 is disposed in a slot 51 formed in the link 42.

The link 42 is connected to the shank 21 within a 3 re-cess 53 by means of the pin 30. The pinf) extends through a tongue S4 of the link 42 and the end of the shank 21, but does not protrude beyond the external surface of the shank 21. The tongue 54 is thicker than the tongue 48. The recess 53` is of rectangular cross-section and prefer-ably has rounded or filleted corners, FIG. 4.

Each of the links 4f), 4l, 42 have similar configurations with the exceptions of the width of the respective tongues 45, 43, 54, and the recesses 51, 46, FIG. 4. This Width or thickness of the tongues 54, 48, 45 is stepped down with the addition of each additional link. It will be readily apparent t-hat as many links may be added as the required strength and diameter of the mandrel will allow. The number of links will therefore vary with the various requirements; it being noted that required strength of each respective link 42, 41, 4h will be reduced as the mandrel 20 is being pulled out of the tube 1t) and the wall of the tube 10' is smoothed. The reason for this is that the link 42 must tow the link 41, and the link 41 must tow the link 4u. The link 4@ must tow only its ball segment 28 which is journaled thereon. The radial shoulder between the journal bearing segments 34 and 44 of each link 4t), 41, 42 keep their respective ball segments 28 from being displaced or pulled off when the mandrel 20 is being removed from the tube 1t), the tube 10 is being pulled off the mandrel 20. With the overlapping of the balls 28, there will be a minimum of wrinkling of the tube wall during bending, particularly at the inside radius of the bend. Accordingly, the strength requirement of the mandrel will be less when the mandrel 2t) is retracted.

As seen in FIG. 2 earch of the tongues S4, 48, 45 are preferably radiused at their ends with their respective pivot pin axis as a radius center. The bottom walls of the slots 53, 5l, 46 are flat. The sides of the tongues 54, 48, 4S are flat and the corresponding side-s o-f the recesses 53, S1, 46 are fiat, FG. 4. The lower surfaces of the tongues 54, 48, 45, FIG. 2, are preferably relieved at a l5 degree angle terminating in a relatively large, low stress radiuses or fillets to accommodate bending of the mandrel Zit downwardly in a single plane to a bending radius less than the diameter of the tube The ball segments' 28 are free to turn or revolve relative to each other. The upper surface of each tongue 54, 48, 45, FIG. 2, is preferably made straight but may be relieved the same as the lower surface if it is desired to have the mandrel bend upwardly as well as downwardly, FIG. 2. The clearances of the various pins, links, shank and ball segments, unless otherwise indicated hereinabove, are preferably suitable for permitting the easy assembly thereof.

It will be understood that this invention may be modified to adapt it to various circumstances and conditions, and it is accordingly desired to comprehend within the purview of this invention such modificati-ons as may be considered to fall within the scope of the appended claims.

What is claimed is:

1. A flexible mandrel comprising,

shank means,

first link means having a journal pivotally connected on a fixed axis to one end of said shank means, first ball segment means turnably journaled on said journal of said first link means,

second link means having a journal pivotally connected on a fixed axis to said first link means,

second ball segment means turnably journaled on said journal of said second link means,

third link means having a journal pivotally connected on a fixed axis to said second link means, and

third ball segment means turnably journaled on said journal of said third link means, and

said link means are formed in such a manner as to permit fiexing of said mandrel in only one plane and in one direction a greater distance than is permitted in an opposite direction. 2. A flexible mandrel comprising, a shank having a spherically-shaped ball end and having a cavity formed in said end, first link means having one end extending into said cavity, pivot pin means extending diametrically through the center of said shank ball end and through said first link means for pivotally connecting said first link means to said shank, said first link means having first and second juxtaposed concentric cylindrical external journal surfaces, and a sphetnica'lly-slraped ball segment having first and second juxtaposed concentric cylindrical internal bearing surfaces corresponding to said journal surfaces of said rst link for journaling said ball segment on said first link,

' said ball segment having a spherically-shaped concavity in one end thereof continuously telescoped over a portion of said sphericallyshaped ball end of said shank, and

said ball segment having a smooth and imperforate external surface.

3. A exible mandrel comprising,

a shank having a spherically-shaped ball end and having a cavity formed in said end,

first link means having one end extending into said cavity,

pivot pin means extending diametrically through the center of said shank ball end and through said first link means for pivotally connecting said first link means to said shank,

said first link means having first and second juxtaposed concentric cylindrical external journal surfaces, and

a spherically-shaped ball segment having first and second juxtaposed concentric cylindrical internal bearing surfaces corresponding to said journal surfaces of said iirst link for journaling said ball segment on said first link,

said ball segment having a spherically-shaped concavity in one end thereof telescoped over a portion of said spherically-shaped ball end of said shank, and

said ball segment having a smooth and imperforate external surface,

second link means having rst and second juxtaposed concentric cylindrical external journal surfaces,

a second spherically-shaped ball segment having first and second juxtaposed concentric cylindrical internal bearing surfaces corresponding to said journal surfaces of said second link means for journaling said second ball segment on said second link means, and

. said second ball segment having a spherically-shaped concavity in one end thereof telescoped over a portion of said first spherically-shaped ball segment,

said second ball segment having a smooth and imperforate external surface,

said first link means having a bifurcated portion disposed within said rst ball segment, and

said second link means having a tongue portion extending into said bifurcated portion, and

second pivot pin means pivotally connecting said tongue portion of said second link means within said bifurcated portion of said first link means,

said second pivot pin means extending diametrically of said first ball segment means parallel to said first p1vot pin means, and

said second pivot pin means being coextensive with said bifurcated portion of said first link means.

4. In a exible mandrel,

link means having first and second juxtaposed concentric cylindrical external journal surfaces, and

a spherically-shaped ball segment having first and second juxtaposed coaxial cylindrical internal bearing surfaces corresponding to said journal surfaces of said link means for journaling said ball segment on said link means about a central aX-is,

said ball segment having a spherically-shaped concavity in one end thereof,

said ball segment having a smooth and imperforate external surface,

said link means having a bifurcated portion on one end thereof,

said link means having a tongue portion on the other end thereof, and

said bifurcated portion and said tongue portion of said link means having parallel pivot pin holes formed therein perpendicularly intersecting said central axis.

References Cited by the Examiner UNITED STATES PATENTS l/l918 11/1927 2/1949 l/1957 12/1959 ll/l960 6/1965 Winterhotf 153--36 Kenney 153-36 Morin 59-78 Zerlaut 153-63 Fuchs 153-63 Condiff 153-63 Spates 72-466 CHARLES W. LANHAM, Primary Examiner.

l W. H. JUST, Examiner. 

1. A FLEXIBLE MANDREL COMPRISING, SHANK MEANS, FIRST LINK MEANS HAVING A JOURNAL PIVOTALLY CONNECTED ON A FIXED AXIS TO ONE END OF SAID SHANK MEANS, FIRST BALL SEGMENT MEANS TURNABLY JOURNALED ON SAID JOURNAL OF SAID FIRST LINK MEANS, SECOND LINK MEANS HAVING A JOURNAL PIVOTALLY CONNECTED ON A FIXED AXIS TO SAID FIRST LINK MEANS, SECOND BALL SEGMENT MEANS TURNABLY JOURNALED ON SAID JOURNAL OF SAID SECOND LINK MEANS, THIRD LINK MEANS HAVING A JOURNAL PIVOTALLY CONNECTED ON A FIXED AXIS TO SAID SECOND LINK MEANS, AND THIRD BALL SEGMENT MEANS TURNABLY JOURNALED ON SAID JOURNAL OF SAID THIRD LINK MEANS, AND SAID LINK MEANS ARE FORMED IN SUCH A MANNER AS TO PERMIT FLEXING OF SAID MANDREL IN ONLY ONE PLANE AND IN ONE DIRECTION A GREATER DISTANCE THAN IS PERMITTED IN AN OPPOSITE DIRECTION. 